A pulse fiber laser device is provided with an amplifying optical fiber and a saturable absorber on a resonant optical path of an optical resonator. Such a laser device is capable of performing mode locking oscillation of the light emitted from the amplifying optical fiber with supplied excitation light in the optical resonator, and outputting a part of the oscillation light to the outside of the optical resonator.
The amplifying optical fiber is used as a laser medium, is an optical fiber in which a rare-earth element such as Yb or Er is added to its core, and by supplying the excitation light of a predetermined wavelength, it is possible to emit light of a predetermined wavelength. The saturable absorber is a substance having a different absorption rate depending on the intensity of the incident light, when the incident light intensity is small, the absorption rate is high, and on the other hand, when the incident light intensity is high, the absorption rate is small and the transmittance is high. Furthermore, when the optical resonator is a Fabry-Perot type resonator reciprocating the light between a first mirror and a second mirror, the saturable absorber is integrated with any of the first mirror and the second mirror to constitute a saturable absorber mirror.
Mode locking is one of ultrashort pulse generation techniques. Mode locking sets up a fixed phase relationship between a plurality of oscillation longitudinal modes simultaneously excited in the amplification band of a laser medium. Mode locking is roughly classified into passive mode locking and active mode locking. A laser device realizing passive mode locking using a saturable absorber can be configured in a simple manner with a small size at a low cost. The saturable absorber used in this case has a function to start mode locking in the optical resonator and stabilize pulse oscillation.
The pulse fiber laser device having an amplifying optical fiber and a saturable absorber arranged on a resonant optical path of an optical resonator and performing mode locking operation can be configured such that a bulk lens is arranged at a space between an end face of the optical fiber and the saturable absorber, and the oscillation light emitted and output from the end face of the optical fiber is converged by the bulk lens and is incident on the saturable absorber. Furthermore, the pulse fiber laser device described in Patent Document 1 is configured such that a saturable absorber mirror is attached to an end face of an optical fiber with the intention of facilitating adjustment of an optical axis.